The Bosch name is synonymous with extremely reliable high performance electric motors - they are the world's largest supplier of automotive components. Bosch produces electric motors for everything from windshield wipers to cordless drills to washing machines, with service centers in virtually every county - their tech support is second to none. Bosch quickly emerged as the cutting edge mid drive motor system from its debut at Eurobike in 2010. Building off the design invented by Panasonic in the mid-90's, they are credited with pioneering the modern advanced mid drive by adding more sensors (torque, cadence, speed and shift), using a single chainring design for better reliability, and an advanced console for more control by the rider that can also estimate the range left in the battery based on mode and terrain. Designed in Germany and assembled in Hungary.
As the most seasoned manufacturer within the eBike industry, they are the motor to beat by the other major motor manufacturers. Brose and Shimano have distinguished themselves by innovating new features that identified Bosch's shortcomings like a comparatively abrupt binary "on-off" power delivery and no integrated battery choices. Trail riders appreciate the system's power, but there are some issues with vulnerable system displays, and bulky motors that can affect handling off road. Bosch still has a decisive edge in overall reliability, mileage per watt hour, a slightly higher maximum power on the top of the line Performance CX, advanced dual battery capabilities, and the smoothest shifting because it is the only of the big three with a real shift sensor. Range prediction is on the conservative side, ensuring you won't come up short. Bosch continues to strike out ahead with bold new technology coming in 2019 like anti-lock braking, and they are coming online with integrated batteries in mid-2018.
Bosch’s signature drive design uses “inside-out” gears - as you turn crank (where the pedals are) it turns a gear inside the motor. Usually on a bike, the crank revolutions are locked to a chainring that then drives the chain to the back wheel. On the Bosch system your pedal force is passed through the motor’s nylon gears, and then back out to the very small chainring that moves independently of the cranks. So one full pedal revolution will turn the outside chainring 2.5 times. Power is the expertly added using sensor data and your mode selection, There are a couple of reasons why they do this - higher motor speeds are much more efficient, saving precious battery power, and better torque for climbing, The chain is tucked away - allowing more ground clearance off road, as well as keeping your pants cleaner. All those gears do make for a subtle but noticeable “whirring” sound that is more pronounced than Brose or Shimano.